The automotive industry has been and continues to go through the evolution of their internal combustion engines in order to have the emissions from these engines lower in hydrocarbons, carbon monoxide and NOx. One source of hydrocarbon emissions has been from the unused fuel within the fuel tank, the carburetor and throughout the fuel delivery system. In order to reduce these emissions, charcoal canisters have been incorporated which absorb the hydrocarbon emissions from the fuel system when the engine is not running. Once the engine is started, the charcoal canister is purged of the absorbed hydrocarbons by virtue of attachment of the charcoal canister to the intake vacuum of the engine which pulls air through the charcoal canister and into the combustion process.
The amount of air which is used to purge the charcoal canisters must be controlled to a specific volume in order for the engine to operate efficiently and be tuned to limit the other types of pollutants. Normally, the regulation of the volume of air flowing through the charcoal canister is controlled by a pulse width modulated solenoid valve and a regulator. The regulator is used to maintain the level of vacuum pressure which is connected to the charcoal canister. Normally the level of this vacuum pressure is maintained at approximately 5 inches of mercury. The solenoid valve is then operated in a pulse width modulated mode to control the amount of fluid allowed to flow through the system at the vacuum pressure level controlled by the regulator. Because the solenoid valve is being operated continuously in a pulse width modulated mode, the noise generated by the solenoid valve must be kept to a minimum in order to provide for the comfort and convenience of the occupants of the vehicle.
Prior art solenoid valves have proved to be excessively noisy for positioning them within the fuel system to meter the flow of air from the charcoal canister. The movable armature has a tendency for side slapping the coil assembly due to the inherent variation in the magnetic flux caused by the tolerances present in the internal components of the prior art solenoid valves. In addition, noise may be generated by the contact between the upper and lower armature if the magnetic flux is strong enough to overcome the amount of force exerted by the coil spring which separates the two armatures.
The present invention provides the art with a solenoid valve which incorporates an elastomeric bushing between the upper and lower armature to dampen any axial motion or contact between the two armatures. In addition, an elastomeric cushion is provided between the movable armature and the coil assembly to cushion any tendency for the moveable armature to slap against the coil assembly. The elastomeric cushion can be a plurality of elastomeric rings surrounding the movable armature or the elastomeric cushion can be a plurality of longitudinally disposed elastomeric strips running the length of the movable armature.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.